Mesoscale disturbance over northern Alaska

April 17th, 2019 |

GOES-17

GOES-17 “Red” Visible (0.64 µm) and Low-level Water Vapor (7.3 µm) images [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) and Low-level Water Vapor (7.3 µm) images (above) showed a mesoscale disturbance that was moving northward over the eastern Brooks Range in far northeastern Alaska on 17 April 2019. The curved configuration of the associated cloud structure suggested that a closed circulation center was present (or had just recently developed) — while surface analyses showed an area of low pressure much farther to the south along the Alaska/Yukon border, there were no features moving northward across the region shown in the GOES-17 imagery.

Light to moderate snow was reported at Arctic Village as this mesoscale disturbance moved over the area (below).

Time series of surface weather observation data from Arctic Village [click to enlarge]

Time series of surface weather observations from Arctic Village [click to enlarge]

375-meter resolution Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2131 and 2313 UTC (below) provided a more detailed view of this feature, in which the clouds exhibited an appearance suggestive of embedded convection. Cloud-top infrared brightness temperatures were as cold as -50ºC just southwest of Arctic Village on the 2313 UTC image — this corresponded to an altitude of 8.5 km on the 00 UTC Fairbanks rawinsonde data.

Suomi NPP VIIRS Day/Night Band (0.7 µm) images at 2131 and 2313 UTC [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) images at 2131 and 2313 UTC [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images at 2131 and 2313 UTC [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images at 2131 and 2313 UTC [click to enlarge]

13-km NAM model fields (below) showed no clear signature of either a closed circulation or a discrete vorticity center — so satellite imagery was depicting the presence of an important feature that was not captured by numerical models. While the 18 UTC model run did show an area of light precipitation moving northward toward the region, the 00 UTC model run scaled back the areal coverage of this precipitation.

3-km NAM 500 hPa height, wind and absolute vorticity [click to enlarge]

3-km NAM 500 hPa height, wind and absolute vorticity [click to enlarge]

3-km NAM Mean Sea Level Pressure and 1-hour accumulated precipitation [click to enlarge]

3-km NAM Mean Sea Level Pressure and 1-hour accumulated precipitation [click to enlarge]

Large ice lead near Utqiagvik (Barrow), Alaska

March 28th, 2019 |

Landsat-8 False Color RGB image at 2222 UTC [click to enlarge]

Landsat-8 False Color RGB images on 21 March and 28 March [click to enlarge]

A toggle between 30-meter resolution Landsat-8 False Color Red-Green-Blue (RGB) images viewed using RealEarth (above) revealed a large ice lead that had opened up to the east of Utqiagvik (Barrow), Alaska on 28 March 2019. Snow and ice appear as darker shades of cyan in the RGB image, with open water exhibiting a dark blue to black appearance.

A sequence of True Color RGB images from NOAA-20 / Suomi NPP VIIRS and Terra MODIS (below) showed the ice lead becoming wider with time during a 5-hour period (note: the time stamps on the images do not reflect the actual time each satellite passed over the Utqiagvik area). The MODIS image appeared the sharpest, since that instrument has a 250-meter resolution in the visible spectral bands (compared to 375 meters for VIIRS).

True Color RGB images from NOAA-20 and Suomi NPP VIIRS and Terra MODIS [click to play animation]

True Color RGB images from NOAA-20 / Suomi NPP VIIRS and Terra MODIS [click to play animation]

In a 14-day series of Terra MODIS composites (below) it can be seen that the same general ice fracture line had opened and closed a few times during the 15-28 March period, depending on the influences of surface wind stress and sea currents. Days with strong and persistent southwesterly winds led to an opening of the ice lead (such as 20 March); however, the largest 1-day change — and the largest opening of the ice lead — occurred from 27-28 March (MODIS | VIIRS), when the strong southwest winds were bringing unseasonably warm air (over 30ºF above normal) across the area. The daily high temperature at Utqiagvik on 28 March was 30ºF, which set a new record high for the date (the normal high temperature for 28 March is -3ºF). Incidentally, this period of above-normal temperatures contributed to Utqiagvik having its warmest March on record.

Daily composites of Terra MODIS True Color RGB images, 15-28 March [click to play animation]

Daily composites of Terra MODIS True Color RGB images, 15-28 March [click to play animation | MP4]

Unusual early ice loss in the Bering Sea

March 9th, 2019 |

GCOM-W2 AMSR2 Sea Ice Concentration, 01 February - 09 March 2019 [click to play animation | MP4]

GCOM-W1 AMSR2 Sea Ice Concentration, 01 February – 09 March 2019 [click to play animation | MP4]

A persistent northward transport of anomalously-warm air across the Bering Sea during the month of February 2019 led to an unusual loss of sea ice there — daily images of GCOM-W1 AMSR2 Sea Ice Concentration (source) from 01 February to 09 March (above) showed the northward retreat of ice from the Bering Sea into the Chukchi Sea. The ice reached its maximum northward extent on 04 March; northward ice motion was very pronounced during the 25-26 February and 27-28 February periods. In early March a synoptic pattern change then allowed cold arctic air to flow back toward the south, helping the ice concentration to begin increasing again in the northern portion of the Bering Sea.

Minimal cloudiness on 28 February allowed the northward flow of ice through the Bering Strait to be seen on GOES-17 (GOES-West) “Red” Visible (0.64 µm) images (below).

GOES-17

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]



Surface features seen in GOES Water Vapor imagery

January 19th, 2019 |
GOES-17 Low-level Water Vapor (7.3 µm) images, plus topography [click to play animation | MP4]

GOES-17 Low-level Water Vapor (7.3 µm) images, plus topography [click to play animation | MP4]

* GOES-17 images shown here are preliminary and non-operational *

A comparison of GOES-17 Low-level Water Vapor (7.3 µm) images with topography (above) revealed that radiation being emitted by the higher elevations of the Brooks Range in northern Alaska was able to be sensed by the 7.3 µm detectors — in spite of the very large satellite viewing angle (or zenith angle) of around 75 degrees.

The GOES-17 ABI Water Vapor band weighting functions calculated using 12 UTC rawinsonde data from Fairbanks, Alaska (below) showed that the presence of cold, dry air within the middle to upper troposphere had shifted the peak pressure of the 7.3 µm weighting function downward to 753.63 hPa (corresponding to an altitude of 7053 feet) — which was at or below the elevation of much of the higher terrain of the Brooks Range. There was very little absorption of upwelling surface radiation by the small amount of water vapor that was present within the middle/upper troposphere, allowing the cold thermal signature of the higher terrain to be observed on the Water Vapor imagery.

GOES-17 Water Vapor weighting functions calculated using 12 UTC rawinsonde data from Fairbanks [click to enlarge]

GOES-17 Water Vapor weighting functions calculated using rawinsonde data from Fairbanks, Alaska [click to enlarge]

On the following day (19 January), a very cold/dry arctic air mass was moving southward across the Upper Midwest and Great Lakes — the coldest temperature in the US that morning (including Alaska) was -42ºF at Kabetogama, Minnesota — and the outline of Lake Superior was very apparent in GOES-16 (GOES-East) Low-level (7.3 µm) and Mid-level (6.9 µm) Water Vapor imagery; in fact, a portion of the northwestern shoreline was even faintly visible in Upper-level (6.2 µm) Water Vapor images (below).

GOES-16 Low-level (7.3 µm), and Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play animation | MP4]

GOES-16 Low-level (7.3 µm), and Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play animation | MP4]

Plots of the GOES-16 Water Vapor band weighting functions calculated using 00 UTC rawinsonde data from International Falls, Minnesota (below) showed some radiation contribution coming from near or just above the surface. As a result, a signature of the strong surface thermal contrast — between a relatively warm Lake Superior (water surface temperatures in the 30s F) and the adjacent cold land surface temperatures (generally -10 to -20ºF) — was able to reach the satellite with minimal absorption by water vapor aloft.

GOES-16 Water Vapor band weighting functions, calculated using rawinsonde data from International Falls, Minnesota [click to enlarge

GOES-16 Water Vapor weighting functions, calculated using rawinsonde data from International Falls, Minnesota [click to enlarge]

===== 21 January Update =====

GOES-16 Low-level (7.3 µm) and Mid-level (6.9 µm) Water Vapor images, with rawinsonde sites plotted in cyan [click to play animation | MP4]

GOES-16 Low-level (7.3 µm) and Mid-level (6.9 µm) Water Vapor images, with rawinsonde sites plotted in cyan [click to play animation | MP4]

In the wake of a large winter storm, arctic air spread across the eastern US on 21 January (minimum temperatures,– and the outline of the coasts of Maryland, Virginia and North Carolina could clearly be seen on GOES-16 Low-level (7.3 µm) Water Vapor images (above). In addition, the coast of the Albemarle-Pamlico Sound  and the Outer Banks of central North Carolina could even be seen for a short time on Mid-level (6.9 µm) Water Vapor imagery (for example, at 1502 UTC).

This cold/dry air mass set new daily records for lowest rawinsonde-measured Total Precipitable Water at Greensboro in central North Carolina (0.04 inch), Roanoke/Blacksburg in western Virginia (0.02 inch) and Wallops Island on the Eastern Shore of Virginia (0.05 inch). GOES-16 Total Precipitable Water product showed values in the 0.01 to 0.09 inch range in the vicinity of Roanoke and Greensboro. In plots of the GOES-16 water vapor weighting functions for those 3 rawinsonde sites (below), note the very strong contributions of radiation directly from or just above the surface for the 7.3 µm and 6.9 µm spectral bands.

GOES-16 water vapor weighting functions, calculated using 12 UTC rawinsonde data from Greensboro, North Carolina [click to enlarge]

GOES-16 water vapor weighting functions, calculated using 12 UTC rawinsonde data from Greensboro, North Carolina [click to enlarge]

GOES-16 water vapor weighting functions, calculated using 12 UTC rawinsonde data from Roanoke/Blacksburg, Virginia [click to enlarge]

GOES-16 water vapor weighting functions, calculated using 12 UTC rawinsonde data from Roanoke/Blacksburg, Virginia [click to enlarge]

GOES-16 water vapor weighting functions, calculated using 12 UTC rawinsonde data from Wallops Island, Virginia [click to enlarge]

GOES-16 water vapor weighting functions, calculated using 12 UTC rawinsonde data from Wallops Island, Virginia [click to enlarge]